The Blue Aura is a juvenile science fiction novel, the nineteenth in Hugh Walters' Chris Godfrey of U.N.E.X.A.
[1] A recent increase in UFO sightings on the island of Guernsey prompts the arrival of the Chris Godfrey and his friends.
They meet 'The Visitors', angelic beings standing seven feet tall, but General Whittle believes the aliens are evil and plans to destroy them with a nuclear missile.
This article about a children's science fiction novel of the 1970s is a stub.
Further suggestions might be found on the article's talk page.